Successful cell division requires positioning of the division plane so that the segregated sets of chromosomes are cleanly partitioned into two separate cells. Furthermore, in some cell types, including stem cells, the division plane must be coordinated with localized cell fate determinants. Errors in division plane positioning can cause chromosome gain or loss, missegregation of cell fate determinants, or a failure of cytokinesis, all of which can accelerate tumor formation. In metazoans, the division plane is determined by the position of the mitotic spindle during anaphase. We have found that two pathways act redundantly and cooperatively to position the division plane. One pathway involves the central spindle and the second involves astral microtubules. The two pathways have been demonstrated to be mechanistically and genetically distinct. To understand the mechanism by which these microtubule-based structures regulate formation of a properly positioned actomyosin-based contractile ring, we will use a multidisciplinary strategy, combining genetic and cell biological analysis in C. elegans embryos and human cells, with biochemistry and live cell imaging. We will address the following questions: How does recruitment of the RhoGEF ECT2 to the central spindle result in local activation of RhoA? Does the cytokinetic scaffold protein anillin modulate the levels of active RhoA and how does the novel protein NOP-1 mediate the organization of contractile ring components? Through what molecular mechanism does high microtubule density inhibit cortical recruitment of myosin? The answers to these questions will provide insights into the mechanism of cell division and other biological processes that involve local regulation of cytoskeletal elements by Rho family of GTPases, such as cell polarization and cell migration. PUBLIC HEALTH RELEVANCE: This project is directed towards understanding how cells multiply, leading to the generation of two daughter cells with appropriate cellular dowries. Progress in this area could improve our understanding of how certain cancers develop and could identify targets for anti-tumor therapies.